The present invention relates to a packaging container, particularly, a packaging tube.
Packaging containers, especially packaging tubes, comprise a tubular body, sometimes also referred to as pipe body, a tube head connected with the tubular body and provided with a discharge (dispenser), and a closure cap that opens and closes the discharge and is attached to the tube head, for instance, by means of a screw thread. Various methods have been developed for the production of packaging containers of the type briefly outlined hereinabove. For example, the tubular bodies may be extruded or co-extruded or, starting from a strip of sheeting, they may be produced by so-called longitudinal seam welding in which the edges of the sheeting strip are joined to each other by the application of heat and pressure and thus form the tubular body. As regards the materials for the tube body, use is made of metals, plastic materials with or without barrier layers and combinations of these materials, the actual choice of material being for the most part governed by the merchandise for which the packaging tube is intended. High-quality goods, such as pharmaceuticals, cosmetics and other body-care means—toothpaste being a case in point—that contain volatile active ingredients or react with gases, call for tubular bodies made of diffusion-resisting materials or material combinations, whereas in the case of less demanding merchandise, such as technical lubricants for example, materials without blockage effect will prove sufficient. The term diffusion is here understood as referring to the migration of volatile components from the interior of the tube towards the outside and vice versa. Once the tube bodies have been produced, they are equipped with heads. This operation can be performed by means of press moulding or injection moulding or by the application of a prefabricated head to the tube body. The plastic materials used for the heads and the tubes have to be compatible, because in each of the named methods the plastic materials of the head and the tube have to flow into each other in order to form the joint. When press moulding is employed, a blank of plasticized plastic material is transformed in a press mould and, while this process is going on, one end of the tube body is also joined to the head that is coming into being. Joining by injection moulding is characterized by the fact that one end of the tube body is joined to the head during the mould-filling process. When a prefabricated head is joined to a tube body, the tube body is attached to the shoulder of a head by means of melting and pressure.
In the case of packaging tubes for high-quality substances, where the tube body is rendered substantially diffusion-resistant by means of an appropriate choice of material, problems are created by the fact that the diffusion resistance of the head has to be made to match that of the tube body. When the previously named head forming and jointing methods are employed, polyolefins, preferably polyethylene (PE) and polypropylene (PP), are used as materials. When this material is used for the head and the tube consists of a laminate, the material of at least one laminate layer, i.e. of one of the cover layers, must be compatible, so that a head-tube joint can be obtained by means of melting and the application of pressure. The aforementioned polyolefins have the advantage that they can be readily jointed, but the drawback that they absorb the volatile components of the packed substances, aromatics among them, with the consequence that the packed substances suffer a quality reduction, and it can also happen that the head disintegrates, as it were, on account of the material consistency becoming soft, i.e. spongy. Gradual disintegration of the material consistency facilitates increased absorption of volatile components and endangers the strength of the joint between head and tube body.
Seals have been developed against this insufficient diffusion resistance. A distinction is made between external seals and internal seals, the former being applied to the external surface of the tube shoulder, the latter to the internal surface of the tube shoulder facing the interior of the tube, covering the shoulder surfaces from the dispenser neck to the joint between tube and head. Seals in the form of annular disks, with a central hole as aperture for the outlet channel, are described as external and internal annular elements according to the place where they are applied. As far as the sealing of tube heads is concerned, external annular elements have not attained the same importance as their internal counterparts. This is due to the fact that, subject to their being made of appropriate materials, they will render the passage of gases (O2, CO2, etc.) from the outside inwards more difficult or even suppress it altogether, but are not effective against the absorption of gaseous components of the packed substances (aromatics, for instance), whereas internal annular elements will perform both these sealing functions, always provided that the internal annular element covers the internal surface of the tube shoulder without jointing defects. A jointing defect is here understood as a folding or waving of the annular element, so that its open sides will not be joined to the surface of the tube shoulder. Jointing defects often lead to fractures of the seals, i.e. the annular elements, in which case there will be no blockage effect at all.
As material for the annular elements, which are produced from film strips, consideration may be given to monofilms (monofilms of plastics or metals), plastic-plastic laminates and plastic-metal laminates. To all intents and purposes, however, only plastic-metal laminates have proved successful among these films, and this for the reason that only annular elements made of this material combination can be joined to the shoulder of a head without jointing defects, while in the case of annular elements made of plastic films, inclusive of plastic laminate films, lack of jointing defects cannot be attained with certainty.
Plastic-metal laminates consist of an aluminium film that is sheathed, i.e. covered on both sides with a polyolefin film. In most cases so-called adhesion promoters are also to be found between the aluminium layer and the polyolefin layers. The aluminium layer or aluminium film serves as barrier layer, and constitutes a highly effective barrier layer against migrations any kind, whereas one polyolefin layer serves as means for joining the annular element to the shoulder surface, the other polyolefin layer as separation of the aluminium layer from the packed material. Though they have the advantages of the defect-free mounting on the head and considerable diffusion resistance, annular elements made of plastic-metal laminates are also associated with disadvantages. The elements are cut or, more precisely, punched from a strip of material. At the cutting or punching edge the metal will be bared and remain uncovered. In the built-in position of the annular element, given a difference between the outer diameter of the element and the inner diameter of the tube body, this metallic part of annular element will not be protected against the packed substance and, depending on the type of substance involved, the metal may lead to contamination of the packed material or the packed material can cause corrosion of the metal layer starting from the metallic cutting edge. Further, films of the type described above are prone to become delaminated between the two covering layers and the intermediate metal layer, starting from the cutting edge. Annular elements made of plastic material do not have the drawbacks of contamination and delamination, but their marked tendency to become folded and wavy constitutes an equivalent disadvantage.
Bearing in mind this prior art, the inventor set himself the object of developing an annular element (i.e. an internal annular element) with which the disadvantages of the known annular elements will be avoided.